SUNIONSTORE for storing results in Redis - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

What is the result of SUNIONSTORE command?

Given two Redis sets:
SET1 contains {"apple", "banana"}
SET2 contains {"banana", "cherry"}
What will be the number of elements in the destination set after running:
SUNIONSTORE dest SET1 SET2?

Redis

SUNIONSTORE dest SET1 SET2

A 3

B 4

C 2

D 1

💡 Hint

SUNIONSTORE stores the union of all members from the given sets into the destination key.

The union of {"apple", "banana"} and {"banana", "cherry"} is {"apple", "banana", "cherry"}, which has 3 elements.

🧠 Conceptual

intermediate

What does SUNIONSTORE do in Redis?

Choose the correct description of the Redis command SUNIONSTORE.

A Adds a member to a set.

B Deletes all members from the specified sets.

C Returns the intersection of multiple sets without storing.

D Stores the union of multiple sets into a new set key.

💡 Hint

SUNIONSTORE combines sets and saves the result.

SUNIONSTORE computes the union of given sets and stores the result in a destination key.

📝 Syntax

advanced

Which SUNIONSTORE command syntax is correct?

Identify the correct Redis SUNIONSTORE command syntax to store the union of sets 'setA' and 'setB' into 'resultSet'.

A SUNIONSTORE resultSet setA setB

B SUNIONSTORE setA setB resultSet

C SUNIONSTORE setA resultSet setB

D SUNIONSTORE resultSet (setA, setB)

💡 Hint

The first argument after SUNIONSTORE is the destination key.

The syntax is SUNIONSTORE destination_key key1 [key2 ...]. Option A follows this order correctly.

❓ optimization

advanced

How to optimize multiple SUNIONSTORE operations?

You need to store the union of three sets: set1, set2, and set3 into 'finalSet'. Which approach is more efficient?

A Run SUNIONSTORE finalSet set1, then SUNIONSTORE finalSet set2, then SUNIONSTORE finalSet set3

B Run SUNIONSTORE tempSet set1 set2, then SUNIONSTORE finalSet tempSet set3

C Run SUNIONSTORE finalSet set1 set2 set3

D Run SUNIONSTORE set1 set2 set3 finalSet

💡 Hint

SUNIONSTORE accepts multiple sets at once.

SUNIONSTORE can take multiple keys to union in one command, which is more efficient than chaining commands.

🔧 Debug

expert

Why does this SUNIONSTORE command fail?

Given the command:
SUNIONSTORE resultSet set1 set2 123
Assuming set1 and set2 are valid sets, why does this command fail?

Redis

SUNIONSTORE resultSet set1 set2 123

A Because all keys must exist before using SUNIONSTORE

B Because '123' is not a valid key name for a set

C Because '123' is interpreted as a number, causing a syntax error

D Because SUNIONSTORE only accepts exactly two sets

💡 Hint

Redis keys can be strings, but numeric strings are allowed if used consistently.

Redis keys can be any string, including numeric strings, so '123' is valid as a key name. The command does not fail for that reason. However, if '123' does not exist as a set, it is treated as an empty set, so no error occurs. The actual failure is if the key is not a set type. But since the question states failure, the only plausible reason is that '123' is not a set type key, causing a type error.